The issue of CO2 cylinders for PFDs has been batted back & forth since 9/11; with the government
position reversing every few months.
that the cartridges are currently allowed, at the discretion of the carrier.
The charged carbon dioxide (CO2) cartridge on the inflatable
is a Hazardous Material as defined by the United States Department of Transportation (USDOT) Hazardous Material Regulation (49CFR175) and also a Dangerous Good as defined by the International Air Transportation Association (IATA). These same rules apply whether you take your inflatable as carry-on or check it through.
The Regulation requires that you declare the hazardous material prior to boarding the aircraft.
There is a 49CFR175.10, Exception 25* in the USDOT Regulation that allows the carriage of a charged inflatable PFD (one PFD per passenger and one spare cartridge), but leaves the final decision to the Individual Air Carriers
whether or not to accept them on the airplanes they own.
IATA has almost identical wording.
*  “With approval of the aircraft operator, one small carbon dioxide cylinder fitted into a self-inflating life-jacket, plus one spare cartridge, may be carried by a passenger or crew member in checked or carry-on baggage.”
Remember these regulations
may not be applied consistently, and may change. If a TSA screener prohibits an inflatable PFD from passing their checkpoint, ask for the supervisor and refer to 49 CFR 175.10 (25).
A check of published company policies produced these results:
* Alaska Airlines
- No mention of self-inflating life jackets in their baggage policy
* Continental Airlines
- Accepts one carbon dioxide (CO2) powered inflatable life jacket as checked or carry-on baggage. The life jacket may be packed in a checked or carry-on bag or carried as a single
item in lieu of a checked or carry-on bag
* American Airlines
- No life jackets inflated by CO2 cartridges allowed
* Delta Airlines
- Accepts one self-inflating life jacket that contains one small carbon dioxide cylinder as checked baggage only
* Northwest Airlines
- CO2 cartridges are allowed in carry on and checked baggage for self-inflating life vests. Two cartridges may be installed in the life vest and two spares may be carried. CO2 cartridges may not be carried for any other purpose.
* Southwest Airlines
- Allows self-inflating life vests with two small gas cylinders and two small spare cylinders in checked baggage